Stent crimping device

ABSTRACT

A system for crimping a prosthesis is disclosed, comprising a plurality of wheels. Each wheel has an outer circumferential surface configured to be placed in contact with the prosthesis. When in contact with the prosthesis, each wheel is configured to be rotated, thereby to apply a radially inward force on the prosthesis so as to reduce the diameter of the prosthesis. More than one set of wheels may be provided, so that the prosthesis is crimped first by one set of wheels, then by a subsequent set of wheels.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus for loading a tubulargraft or prosthesis, such as a stent, onto the distal end of a catheterassembly of the kind used, for example, in percutaneous transluminalcoronary angioplasty (PTCA) or percutaneous transluminal angioplasty(PTA) procedures.

In typical PTCA procedures, a guiding catheter is percutaneouslyintroduced into the cardiovascular system of a patient through thebrachial or femoral arteries and advanced through the vasculature untilthe distal end of the guiding catheter is in the ostium. A guide wireand a dilatation catheter having a balloon on the distal end areintroduced through the guiding catheter with the guide wire slidingwithin the dilatation catheter. The guide wire is first advanced out ofthe guiding catheter into the patient's coronary vasculature and thedilatation catheter is advanced over the previously advanced guide wireuntil the dilatation balloon is properly positioned across the arteriallesion. Once in position across the lesion, a flexible and expandableballoon is inflated to a predetermined size with a radiopaque liquid atrelatively high pressures to radially compress the atheroscleroticplaque of the lesion against the inside of the artery wall and therebydilate the lumen of the artery. The balloon is then deflated to a smallprofile so that the dilatation catheter can be withdrawn from thepatient's vasculature and the blood flow resumed through the dilatedartery. As should be appreciated by those skilled in the art, while theabove-described procedure is typical, it is not the only method used inangioplasty.

In angioplasty procedures of the kind referenced above, restenosis ofthe artery may develop over time, which may require another angioplastyprocedure, a surgical bypass operation, or some other method ofrepairing or strengthening the area. To reduce the likelihood of thedevelopment of restenosis and to strengthen the area, a physician canimplant an intravascular prosthesis for maintaining vascular patency,commonly known as a stent, inside the artery at the lesion. The stent iscrimped tightly onto the balloon portion of the catheter and transportedin its delivery diameter through the patient's vasculature. At thedeployment site, the stent is expanded to a larger diameter, often byinflating the balloon portion of the catheter. The stent also may be ofthe self-expanding type.

Since the catheter and stent travel through the patient's vasculature,and probably through the coronary arteries, the stent must have a smalldelivery diameter and must be firmly attached to the catheter until thephysician is ready to implant it. Thus, the stent must be loaded ontothe catheter so that it does not interfere with delivery, and it mustnot come off the catheter until it is implanted.

In procedures where the stent is placed over the balloon portion of thecatheter, it is necessary to crimp the stent onto the balloon portion toreduce its diameter and to prevent it from sliding off the catheter whenthe catheter is advanced through the patient's vasculature. Non-uniformcrimping can result in sharp edges being formed along the now unevensurface of the crimped stent. Furthermore, non-uniform stent crimpingmay not achieve the desired minimal profile for the stent and catheterassembly. Where the stent is not reliably crimped onto the catheter, thestent may slide off the catheter and into the patient's vasculatureprematurely as a loose foreign body, possibly causing obstructedarteries, blood clots in the vasculature, including thrombosis.Therefore, it is important to ensure the proper crimping of a stent ontoa catheter in a uniform and reliable manner.

This crimping is often done by hand, which can be unsatisfactory due tothe uneven application of force resulting in non-uniform crimps orloosely fitted stents which pose a critical danger to the patient. Inaddition, it is difficult to visually judge when a uniform and reliablecrimp has been applied.

Some self-expanding stents are difficult to load by hand onto a deliverydevice such as a catheter. Furthermore, the more the stent is handledthe higher the likelihood of human error, which would be antithetical toa properly crimped stent. Accordingly, there is a need in the art for adevice for reliably crimping a stent onto a catheter.

There have been attempts at devising a tool for crimping a stent onto aballoon delivery catheter. An example of such a tool comprises a seriesof plates having substantially flat and parallel surfaces that move in arectilinear fashion with respect to each other. A stent carryingcatheter is disposed between these surfaces, which surfaces crimp thestent onto the outside of the catheter by their relative motion andapplied pressure. The plates have multiple degrees of freedom and mayhave force-indicating transducers to measure and indicate the forceapplied to the catheter during crimping of the stent.

Another stent loading tool design is comprised of a tubular memberhousing a bladder. The tubular member and bladder are constructed tohold a stent that is to be crimped onto a balloon catheter assembly.Upon placement of the stent over the balloon portion of the catheter, avalve in the loading tool is activated to inflate the bladder. Thebladder compresses the stent radially inward to a reduced diameter ontothe balloon portion of the catheter to achieve a snug fit. In this way,the stent is crimped onto the distal end of a balloon catheter with aminimum of human handling. The foregoing stent crimping tools aredisclosed in, for example, U.S. Pat. Nos. 5,437,083 and 5,546,646 toWilliams et al.

Still another conventional stent crimping tool is manufactured byJOHNSON & JOHNSON and appears similar to a hinged nutcracker.Specifically, the tool is comprised of two hand operated levers hingedat one end and gripped in the palm of the hand at the opposite end. Acylindrical opening holding a crimping tube is provided through themid-portion of the tool to receive therein a stent loaded onto a ballooncatheter. The crimping operation is performed by the user squeezing thehandle thereby pressing the crimping tube which in turn pinches thestent onto the balloon catheter.

While the prior art devices are suitable for crimping stents ontoballoon catheters, they suffer from problems such as non-uniformcrimping forces, especially for long stents, resulting in non-uniformcrimps. The present invention addresses these and other needs.

SUMMARY OF THE INVENTION

Both PTCA and PTA procedures have become commonplace in treatingstenoses or lesions in blood vessels and coronary arteries. Inapproximately 35% to 40% of the procedures, restenosis may developrequiring a further angioplasty, atherectomy or bypass procedure toreturn the patency of the vessel. Intravascular stents are now beingdeployed after PTCA and PTA procedures, and after atherectomies, inorder to help prevent the development of restenosis. Importantly, suchstents, mounted on the balloon portion of a catheter, must be tightlycrimped to provide a low profile delivery diameter, and to ensure thatthe stent stays on the balloon until the balloon is expanded and thestent is implanted in the vessel. The present invention is directed to acrimping tool that can repeatedly provide a uniform and tight crimp toensure the low profile diameter of the stent on the balloon portion ofthe catheter, and to ensure that the stent remains firmly attached untilit is implanted in the vessel by expanding the balloon.

More precisely, the present invention is directed to a tool for crimpinga prosthesis onto a catheter comprising a plurality of wheels, whereineach wheel is rotatably mounted on an axle. Each wheel has an outercircumferential surface configured to apply a radially inward force onthe prosthesis. The wheels are mounted so as to be positionable inrelation to each other such that a diameter of each wheel radiatesoutwardly from a central axis, wherein the outer circumferentialsurfaces of the wheels are positionable equidistant from the axis by afirst smallest possible distance to define a first space that includesthe axis. This configuration permits a prosthesis to be passed betweenthe wheels which in apply a radially inward force on the prosthesis tocrimp the prosthesis to a smaller diameter. A first number out of theplurality of wheels are mounted so as to be restrained from furtheradvancing toward the axis, thereby leaving a number of remaining wheelsmounted to be capable of further advancing toward the axis, wherein theouter circumferential surfaces of the remaining wheels are positionableequidistant from the axis by a second smallest possible distance todefine a second space that includes the axis, the second space beingsmaller than the first space. In this way, the remaining wheels areadvantageously positioned to further crimp the prosthesis to an evensmaller diameter, which would otherwise be impossible if the firstnumber of wheels were not configured to be restrained from furtheradvancing toward the axis.

In another aspect, the invention includes a method of crimping aprosthesis having an elongate axis. The method comprises positioning aplurality of wheels about the prosthesis so that an outercircumferential surface of each wheel is in contact with the prosthesis;moving the prosthesis along the elongate axis; rotating each of thewheels while maintaining contact between the wheels and the prosthesis,thereby reducing the diameter of the prosthesis; causing a first numberof the wheels to no longer be in contact with the prosthesis to leave afirst remainder of wheels in contact with the prosthesis; and rotatingeach of the first remainder of wheels while maintaining contact betweeneach of the first remaining wheels and the prosthesis, thereby furtherreducing the diameter of the prosthesis. This method has a similaradvantage to the foregoing apparatus, of sequentially crimping theprosthesis to a final diameter, using a first number of wheels and thensubsequently a second smaller number of wheels to finish off thecrimping to the desired final diameter.

In yet a further aspect, the invention includes a system for crimping aprosthesis having an elongate axis comprising a first plurality ofwheels, wherein each wheel is rotatably mounted on an axle and eachwheel has an outer circumferential surface having a first width. Thewheels are configured to be positionable in relation to each other suchthat a diameter of each wheel radiates outwardly from a central axis,whereby the outer circumferential surfaces of the wheels define a firstspace that includes the central axis, the first space being configuredto receive the prosthesis during crimping. A second plurality of wheelsis provided, wherein each wheel is rotatably mounted on an axle and eachwheel has an outer circumferential surface having a second width. Thesecond plurality of wheels are configured to be positionable in relationto each other such that a diameter of each wheel radiates outwardly fromthe central axis, whereby the outer circumferential surfaces of thesecond plurality of wheels define a second space that includes thecentral axis, the second space being configured to receive theprosthesis during crimping. Significantly, in this embodiment, the firstwidth is greater than the second width, thereby allowing the secondplurality of wheels to take the prosthesis down to a smaller diameterthan the first plurality of wheels can reasonably achieve.

And in yet a further aspect, the invention includes a method of crimpinga prosthesis having an elongate axis. The method comprises positioning afirst plurality of wheels about the prosthesis so that an outercircumferential surface of each wheel is in contact with the prosthesis,each surface having a first width; moving the prosthesis along theelongate axis; rotating each of the wheels while maintaining contactbetween the wheels and the prosthesis, thereby reducing the diameter ofthe prosthesis. Then, removing all of the first plurality of wheels frombeing in contact with the prosthesis; positioning a second plurality ofwheels about the prosthesis so that an outer circumferential surface ofeach of the second plurality is in contact with the prosthesis, eachsurface having a second width less than the first width; moving theprosthesis along the elongate axis; rotating each of the secondplurality of wheels while maintaining contact between the secondplurality of wheels and the prosthesis, thereby further reducing thediameter of the prosthesis.

An even further aspect of the invention includes a system for crimping aprosthesis comprising a first plurality of wheels, wherein each wheel isrotatably mounted on an axle, and each axle of the first plurality liesin the same first plane. Each wheel has an outer circumferential surfaceand the wheels are positioned in relation to each other such that adiameter of each wheel radiates outwardly from a central axis, wherebythe outer circumferential surfaces of the wheels define a first spacethat includes the central axis, the first space being configured toreceive the prosthesis during crimping. A second plurality of wheels isprovided wherein each wheel is rotatably mounted on an axle, and eachaxle of the second plurality lies in the same second plane, the secondplane being spaced apart from the first plane by a distance. Each wheelhas an outer circumferential surface and the wheels are positioned inrelation to each other such that a diameter of each wheel radiatesoutwardly from the central axis, whereby the outer circumferentialsurfaces of the wheels define a second space that includes the centralaxis, the second space being configured to receive the prosthesis duringcrimping. Significantly, the first space is larger than the secondspace. By this structure, a prosthesis may advantageously be crimpedwhen the prosthesis is unusually long. The spaced apart sets of wheelsallow for greater control over the crimping process as the prosthesispasses from one set to the next.

Finally, the invention includes a method of crimping a prosthesis havingan elongate axis comprising moving the prosthesis along its axis betweena first plurality of wheels so that an outer circumferential surface ofeach of the first plurality of wheels is in contact with the prosthesis;rotating each of the wheels while maintaining contact between the wheelsand the prosthesis, thereby reducing the diameter of the prosthesis by afirst amount; passing the prosthesis from between the first plurality ofwheels to between a second plurality of wheels, the second plurality ofwheels being situated adjacent the first plurality; moving theprosthesis between the second plurality of wheels so that an outercircumferential surface of each of the second plurality of wheels is incontact with the prosthesis; rotating each of the second plurality ofwheels while maintaining contact between the wheels and the prosthesis,thereby further reducing the diameter of the prosthesis by a secondamount. In this embodiment, the invention has advantages similar tothose of the previously described embodiment, in which a long prosthesismay be crimped under improved control of one set of wheels adjacent asecond set of wheels.

The present invention is thus capable of homogeneously and preciselycrimping a stent onto a balloon catheter. Such a crimping tool is highlyuseful to cardiologists and radiologists, for example. Such physiciansare constantly concerned with proper deployment of the stent within thepatient that it is desirable to have a consistently and reliably crimpedstent. The present invention tool is further a time saver, because thestent crimping procedure can be performed fairly efficiently andquickly. Indeed, these and other advantages of the present inventionwill become apparent from the following detailed description thereofwhen taken in conjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic side elevational view, partially in section,depicting a stent that has been crimped onto a delivery catheter anddisposed within a vessel.

FIG. 2 a shows a schematic top plan view of a first embodiment of thepresent invention stent crimping system employing nine radiallydistributed wheels, with the wheels set in a first position.

FIG. 2 b shows a detail from FIG. 2 a, as indicated.

FIG. 3 a shows a schematic top plan view of the embodiment of FIGS. 2 aand b, with the wheels set in a second position.

FIG. 3 b shows a detail from FIG. 3 a, as indicated.

FIG. 4 shows a schematic partial top plan view of a second embodiment ofthe present invention, showing features of the invention, with wheelsset in a first position.

FIG. 5 shows a partial top plan view of the embodiment of FIG. 4,showing the wheels set in a second position.

FIG. 6 shows a partial top plan view of the embodiment of FIG. 4,showing the wheels set in a third position.

FIG. 7 shows a partial top plan view of the embodiment of FIG. 4,showing the wheels set in a fourth position.

FIG. 8 shows a schematic partial side view of a third embodiment of theinvention, showing features of the invention.

FIG. 9 shows a schematic bottom view of the embodiment of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 2-9, there is shown by way of exemplificationand not limitation a prosthesis or stent crimping device having featuresof the present invention, generally indicated by the numeral 22.

Before the invention is described, several aspects of related technologyand human anatomy are described with reference to FIG. 1, whichillustrates an intravascular stent 10 which is mounted onto a deliverycatheter 11. The stent 10 generally comprises a plurality of radiallyexpandable cylindrical elements 12 disposed generally coaxially andinterconnected by members 13 disposed between adjacent cylindricalelements 12. Delivery catheter 11 has an expandable portion or balloon14 for expanding stent 10 within coronary artery 15 or other vessel suchas saphenous veins, carotid arteries, arteries, and veins. Artery 15, asshown in FIG. 1, has a dissected lining 16 which has occluded a portionof the arterial passageway.

The delivery catheter 11 onto which the stent 10 is mounted isessentially the same as a conventional balloon dilatation catheter forangioplasty procedures. The balloon 14 may be formed of suitablematerials such as polyethylene, polyvinyl chloride, polyethyleneterephthalate, nylon and other like polymers. In order for the stent 10to remain in place on balloon 14 during delivery to the site of thedamage within artery 15, the stent 10 is compressed onto balloon 14.This compressing step is known as crimping.

An optional retractable protective delivery sleeve 20 may be provided tofurther ensure that stent 10 stays in place on balloon 14 of deliverycatheter 11 and to prevent abrasion of the body lumen by the opensurface of stent 10 during delivery to the desired arterial location.Other means for securing stent 10 onto balloon 14 may also be used, suchas providing collars or ridges on the ends of the working portion, i.e.,the cylindrical portion of balloon 14.

In order to implant stent 10, it is first mounted onto inflation balloon14 on the distal extremity of delivery catheter 11. Stent 10 is crimpeddown onto balloon 14 to ensure a low profile. The present inventionaddresses this crimping procedure by describing a system and method forthe same.

The catheter-stent assembly can be introduced into the patient'svasculature through processes known in the art. Briefly, guide wire 18is disposed across the arterial section where an angioplasty oratherectomy has been performed requiring a follow-up stenting procedure.In some cases, the arterial wall lining may be detached so that guidewire 18 is advanced past detached or dissected lining 16 and thecatheter-stent assembly is advanced over guide wire 18 within artery 15until stent 10 is directly under detached lining 16. Prior to inflationof balloon 14, delivery sleeve 20 is retracted to expose stent 10.Depending on the balloon and stent assembly, a delivery sleeve may beunnecessary. Balloon 14 of delivery catheter 11 is then inflated usingan inflation fluid. Expansion of balloon 14 in turn expands stent 10against artery 15. Next, balloon 14 is deflated and catheter 11 iswithdrawn leaving stent 10 to support the damaged arterial section. Asmentioned above, in order to ensure proper seating of stent 10 onballoon 14, and to ensure proper deployment of stent 10 at the site ofthe damage within artery 15, the stent crimping procedure is important.

FIGS. 2 a and 2 b show a schematic top plan view, and detail, of asystem or device exemplifying a preferred embodiment of the presentinvention stent crimping tool 22. As recognized in this top plan view,the present invention stent crimping tool 22 is characterized by aplurality of wheels 24 a, 24 b, 24 c, 24 d, 24 e, 24 f, 24 g, 24 h, 24i, arranged about a central axis A-A (extending perpendicularly into thepage, as seen in FIG. 2). Preferably, the wheels are arranged evenlyabout the axis A-A. Each wheel defines its own central plane 26 a, . . .26 i. The wheels are arranged so that the plane of each wheel passesthrough the central axis A-A, and extends radially outwardly from thecentral axis. Each wheel is configured to rotate about its own axle 28a, . . . 28 i. All of the axles lie in a common plane through which theaxis A-A perpendicularly passes. Each wheel has an outer circumferentialsurface 30, best seen in FIG. 2 b. These surfaces face toward the axisA-A, and define a space 32 between them. While nine wheels are shown inthis embodiment, other numbers of wheels are contemplated to be withinthe scope of the invention.

Once the wheels are assembled as described and shown, a stent to becrimped is positioned in relation to the wheels. Such stent 10 ispositioned coaxial with the axis A-A. The stent is positioned upon acatheter (not shown in FIGS. 2-9) onto which the stent is to be crimped.The catheter may take any of the forms described herein, includingballoon catheter, non-balloon catheter etc. The manner in which thestent is crimped using the system of the present invention may takeplace under a number of preferred embodiments. In each embodiment, thegeneral principle is applied that the outer surface 30 of each of aplurality of wheels is positioned against the stent, which is held withits own axis co-axial with the axis A-A. At least one wheel may bedriven to rotate. The other wheels may either be driven, or as will beappreciated, they may rotate in unison with the driven wheel due totheir contact with the stent that is forced to move axially in responseto the rotated wheel. The rotation of the wheels, and the frictionbetween the surfaces 30 and the stent, causes the stent to move axiallyalong axis A-A. Thus, each wheel applies a radially inward force on thestent. The magnitude of this inward force will depend on the size of thespace 32 that has been selected to be formed between the surfaces 30 ofthe wheels 24 a, etc., in relation to the size of the stent 10. Theseforces gradually move axially along the length of the stent as the stentpasses between the wheels along axis A-A. It will be appreciated thatthe plurality of wheels effectively surround the stent, so that thestent experiences a circumferentially inward force that gradually movesalong the length of the stent axis. This application ofcircumferentially inward forces along the axis of the stent has theeffect of uniformly crimping the stent radially inwardly onto thecatheter, after which catheter and stent 10 are removed for furthertreatment and/or processing in which an outer sheath such as sheath 20(FIG. 1) may be fitted over the outside of the stent, and the like.

Turning now to aspects of different preferred embodiments under whichthe above described general application of radially inward forces may beapplied to the stent. Referring to FIG. 2, there is first seen how anuncrimped stent 10, with an original uncrimped diameter, is positionedbetween nine wheels 24 a-24 i arranged equidistantly about the axis A-Aof the stent. The external circumferential surface 30 of each wheel ispositioned adjacent the stent to form a space 32 between the wheelsthat, in use, includes the stent. Preferably, the stent is positioned ona catheter that is supported by a mandrel or guidewire (not shown) tosupport the catheter and balloon as the stent is crimped. By supportingand moving the mandrel, the stent itself may be supported and moved inrelation to the wheels. To commence the crimping process, one or morewheels are rotated under power, and the stent is fed (by manipulatingthe mandrel) into the space 32 between the wheels. It should beappreciated that the size of the space 32 will be judiciously selectedto approximate the diameter of the stent that is desired after a firstpass between the wheels. Although, it should be appreciated, it isnecessary for only one wheel to be driven or rotated under power, in apreferred embodiment all the wheels are rotated under power to provide auniformly crimped stent configuration. Rotation of the wheels isconfigured in relation to the mandrel to be accompanied by relativeaxial movement of the stent at the same velocity as the tangentialvelocity of the wheels at their points of contact with the stent. Thisaspect allows the stent to receive a radially inward force applied byeach wheel without any shear force being exerted at the surface of thestent. Where only one wheel is driven, this driven rotation will, due tothe contact by all of the wheels with the stent, cause the other wheelsalso to rotate as the stent moves past the remaining undriven wheels.

It should be appreciated that by merely passing the stent once throughthe space 32 between the wheels while they are under rotation will notnecessarily impart a crimped diameter of desired magnitude to the stent.This is firstly because a certain amount of elastic recovery may beachieved by the stent once it has passed between the wheels, andsecondly because it may be undesirable to impart the final desiredcrimped diameter in one pass. Thus, a second pass in the otherdirection, and even a third pass, may be desired to bring the stent to adesired uniform diameter, while the space between the wheels is heldunder a constant geometry or slightly reducing geometry. Once the stenthas achieved a desired diameter, the space 32 between the wheels may bereduced in size by moving the wheels in unison closer toward the axisA-A so that they remain equidistant from the axis. Yet again, thediameter of the stent may be reduced by a series of passes through thespace 32 while the wheels are driven to apply a radially inward force onthe stent (the force effectively extending around the circumference ofthe stent), while the force moves axially up and down the exterior ofthe stent in the absence of any surface shear force.

It will be further appreciated that there is a limiting factor in howsmall the space 32 may be reduced by advancing the wheels toward theaxis A-A is the width of the wheels, because there may come a pointwhere the space 32 cannot be made any smaller by advancing the wheelstoward the axis A-A in that the wheels may tend to butt up against eachother and prevent further reduction of the space 32. Desirably, on theone hand, the width of the wheels should not be too narrow because awheel may apply too narrow a load on the stent, capable of bending thestent locally rather than crimping it. On the other hand, a broader setof wheels results in a large minimum space 32 which may be larger thandesired. Thus, in yet another aspect of the invention, exemplified inFIG. 3, the wheels are mounted on their axles to permit some of thewheels 24 b, 24 c, 24 e, 24 f, 24 h, 24 i so that they cease advancingin unison towards the axis A-A, or they even be moved away from the axisA-A. By ceasing the advance of, or removing, some of the wheels, theremaining wheels 24 a, 24 d, 24 g can be moved even closer toward theaxis A-A unhindered. Thus, as exemplified in FIG. 3, in a preferredembodiment, three of the nine wheels may initially be held stationarywith respect to the axis A-A, or be moved away from the axis A-A,leaving six wheels to form the much reduced space 32 through which thestent must pass for crimping under the radially inward force of theremaining wheels. Subsequently, another three wheels may be held back orretracted, leaving only three wheels to form an even more reduced space32 through which the stent must pass for crimping. Therefore, byconfiguring the mounting of each wheel to selectively permit some wheelsto be held back from the axis A-A or retracted, a system is providedthat advantageously allows the remaining wheels to finish off thecrimping process when the stent has reached its smallest diameter.

Turning now to another aspect of the invention, there is shown withreference to FIGS. 4-7 how a plurality of wheels may be configured toprovide a graduated crimping effect using a different embodiment thanthe one described above. In this embodiment, nine wheels 25 a-25 i (asseen in FIG. 4) each may have the same diameter as in the previousembodiment, but different sets of wheels may have different widths, indecreasing magnitude. Thus, for example, of the nine wheels, in a firstset of three wheels 25 i, 25 c, 25 f (as seen in FIG. 5) each wheel hasa circumferential surface 30 with a broadest width, in a second set ofthree wheels 25 a, 25 d, 25 g (as seen in FIG. 6) each wheel has acircumferential surface 30′ with a narrower width, and in a third set ofthree wheels 25 b, 25 e, 25 h (as seen in FIG. 7) each wheel has acircumferential surface 30″ with a narrowest width.

This second embodiment operates differently than the first embodiment inthat only one set of three wheels is deployed in a crimping action atany one time. The broadest set is used first as exemplified in FIG. 5,when the stent 10 is in its largest uncrimped diameter. Preferably, theouter circumferential surface 30 of each wheel may be given a slightcurvature along its width, to conform with the diameter of the stent. Itwill be appreciated that the diameter of the stent will move from afirst diameter to a second smaller diameter as it undergoes crimpingwith the first set of wheels, so the curvature of the surface on theouter wheel circumference may preferably be chosen to conform with themidpoint diameter of the stent, lying half way between the first and thesecond diameters. Thus, in operation, the first set of three wheels arebrought together to provide a first space 32 between them (FIG. 5). Thestent is then passed into the space and the wheels are set in motion. Asbefore, a radially inward force is applied to the stent by the wheels,but in this embodiment, there are only three wheels applying the forceinitially, each force occupying a broader extent of the stentcircumference. Preferably, the width of the wheels is set to provide asubstantially uniform force around the circumference of the stent. Asbefore, the stent may be manipulated via a mandrel extending through thecatheter, and the stent may be passed back and forth through the spacewhile the wheels turn.

Once the first set of wheels have imparted a desired crimped diameter tothe stent, the first set of wheels 24 i, 24 c, 24 f (FIG. 5) may bewithdrawn, and the second set 24 a, 24 d, 24 g (FIG. 6), having anarrower width, are moved up toward the axis A-A to provide a secondspace 32′ between them. It will be appreciated that a narrower set ofwheels is capable of forming a second space that is smaller than thefirst space 32. In the same way, a slight curvature may be imparted tothe outer circumferential surface 30′ of the second set of wheels alongits width, the curvature being chosen to conform with a diameter of thestent between the range of diameters it will assume while undergoingcrimping. As with the first set of wheels, the second set of wheels isused to further crimp the stent down to a smaller overall diameter.

Finally, if the crimping thus done is not sufficient, the second set ofwheels may be withdrawn, and the third set of wheels 24 b, 24 e, 24 h(FIG. 7), having a yet narrower width than the second set, are moved uptoward the axis A-A to provide a third space 32″ between them that issmaller than the second space 32′. Likewise, a curvature may be impartedto the outer circumferential surface 30″ of the third set of wheelsalong their width. By following the same procedure as before, a finaldesired crimped diameter may be imparted to the stent with minimaltrauma to the underlying catheter and/or balloon. Of course, furtherwheel sets may be added to the third set, as required.

Turning now to a third embodiment of the invention, a final aspect ofthe invention is described with reference to FIGS. 8-9. In thisembodiment, principles similar to those of the previous embodiments areemployed. However, instead of moving sets of wheels toward and away fromthe stent after each progressive crimping action, as in the previousembodiment, in this third embodiment, sets of wheels are placed in fixedposition, one set stacked vertically under the other and spacedvertically apart from the one above, by a certain distance. Although thewheels are preferably in fixed position during a crimping operation, thewheels may be adjusted both vertically (i.e. one set towards or awayfrom another set) and radially (i.e., towards or away from the axis A-A)as required.

As exemplified in FIGS. 8 and 9, a first set 102 of wheels 40 h, 40 b,40 e (wheel 40 e is not seen in FIG. 8) is positioned about a centralaxis A-A, each wheel lying in its own plane 42 h, 42 b, 42 e (FIG. 9)that radiates outwardly from the axis to leave a small space 132 betweenthe wheels. Each wheel turns upon its own axle 44 h, 44 b, 44 e etc.Each axle of the first set of wheels lies in the same first plane. Acircumferential surface 130 of each wheel faces toward the axis A-A. Asin the previous embodiment, the surface 130 may be curved to accommodatethe radius of a stent, and the width of the wheels may be reduced fromone set to the next, as explained below. Preferably, but notnecessarily, three wheels are included in each set. Other numbers ofwheels per set are considered to be within the scope of the invention.In the first set, the wheels are positioned sufficiently far apart fromthe axis A-A that the space 132 is large enough to receive an unexpandedstent loaded onto a mandrel with guidewire (not shown), and to allow theloaded stent to pass through the space 132 while moving downward alongthe axis A-A. The size of the space 132 may be adjusted by setting thewheels apart a desired distance, and then fixing the distance duringcrimping operations. As in the previous embodiment, movement of thestent along the axis A-A may be achieved by manipulating the mandrel (orguidewire) onto which the stent is loaded. The space 132 is sized sothat, as the stent is passed through the space 132 between the wheels,the stent is radially compressed from its first uncompressed diameter 46to a second smaller diameter 48. Such compression may either result inplastic deformation of the elements of the stent so that the stentassumes a permanently reduced diameter, or (in the case of a selfexpanding stent) it may result in elastic compression of the stent whichis impermanent. Further alternatively, such compression may be appliedto a stent made of memory alloy such as Nitinol.

With further reference to FIGS. 8 and 9, a second set 104 of wheels 44i, 44 c, 44 f (wheel 44 i is not seen in FIG. 8) is positioned below thefirst set 102, in that each axle of the second set of wheels lies in thesame second plane that is spaced below the first plane. The mounting ofthe wheels on their axles is such that the vertical distance Dl betweenthe first set 102 and the second set 104 of wheels is preferably capableof being adjusted. But once the desired distance between the two wheelsets is achieved for use, that distance is preferably held fixed. Thesecond wheel set, like the first set, comprises a number of wheels(preferably numbering three) all radiating outwardly from the axis A-A.Each wheel has a circumferential surface 130′ that faces the axis A-A,and that is curved to accommodate the radius of a stent, and the widthof the wheels of the second set may be narrow than that of the firstset. The wheel faces 130′ define a space 132′ that is smaller than thespace 132, and may be adjusted to a desired size before crimpingoperations. In order to permit the second set of wheels to be positionedclose to the first set (so that D1 may be a short distance), the wheelsof each set are offset from each other by about 40-80 degrees about axisA-A (as seen in FIG. 9) so that, when viewed from the side (as in FIG.8), the wheels of the one set may vertically overlap with the wheels ofthe next set, yet not collide with each other.

In similar fashion, a third set 106 of wheels 44 a, 44 d, 44 g (wheel 44d is not seen in FIG. 8) is positioned a vertical distance D2 below thesecond set, in that each axle of the third set of wheels lies in thesame third plane that is spaced D2 below the second plane. Again, thisvertical distance is capable of being adjusted, and fixed once thedesired distance is satisfactory. The third set of wheels adjustablydefines a space 132″ between them that is smaller than space 132′.Again, the vertical distance D2 may be reduced to a desired amount byoff-setting the third set 106 of wheels from both the first set and thesecond set (as best seen FIG. 9).

Once a plurality of wheel sets are arranged in a spaced apart verticalrelationship to each other as described, the device is used as follows.A stent or prosthesis is mounted onto a catheter or mandrel (not shown),that may include a guidewire. Manipulation and movement of the stent isachieved by manipulating the mandrel or catheter upon which the stent ismounted. The catheter (preferably, on a guidewire) is threadedsequentially through the spaces 132, 132′ and 132″ to extend coaxiallywith the axis A-A. At least one wheel of each set may then be drivenunder power, although preferably all wheels may be driven to provide auniformly crimped stent. The mounted stent is then fed downwardlythrough the first space 132 where the rotating wheels impart a firstcrimping effect from radially inward force applied by the wheels, andreduce the diameter of the stent from its original uncrimped diameter 46to a smaller second diameter 48 that includes some degree of crimping. Ashort distance after emerging from the space 132 between the first setof wheels, the stent passes through the second space 132′ between thesecond set of wheels, where the stent receives another incrementalcrimping force by which its diameter is further reduced to a thirddiameter 50. Then, a short distance after emerging from the second space132′ between the second set 104 of wheels, the prosthesis passes throughthe third space 132″ between the third set 106 of wheels where itreceives yet another incremental crimping by which its diameter is yetfurther reduced to a fourth diameter 52. In a preferred embodiment,three sets of wheels are provided, although more or fewer sets may beprovided where needed to achieve the desired degree of crimping.

When the stent finally passes downwardly from the space 132″ defined bythe last set of wheels 106, it may be passed into a sheath 20 (such asseen in FIG. 1) or containment means configured to hold the stentsecurely on the catheter. It will be appreciated that in the case of aself expanding stent this is a necessary step to finalizing the crimpingprocess. In the case of a balloon expanded stent, a sheath is ofteninstalled to cover the stent during delivery through a body lumen, sothat the stent does not injure the walls of the lumen as it passesthrough the lumen. Passing the crimped stent mounted on a catheter intoa sheath may be achieved by known means (not shown), wherein the sheathis slightly heated, then passed over a cylinder that is in turn passedover the stent mounted on catheter. The cylinder may be removed, leavingthe sheath to surround the stent. Subsequent retraction of the sheathfrom the stent allows the stent free to be deployed, whether by selfexpanding means or by balloon expanding means.

It will be appreciated that the vertical distance separating one set ofwheels from the next (e.g. D1, D2) will depend on a number of factors.For example, if the stent or prosthesis is to be plastically deformed bypassage between the wheel sets, the vertical distance between wheel setsmay be longer than if the stent is self-expanding. Another factor is therequired diameter of the stent, both before and after passage betweenthe wheels. Ultimately, the optimal distance of separation between wheelsets may be determined by experimentation, to achieve the desired degreeof crimping by each wheel set so that the starting diameter is reducedto the desired final reduced diameter without excessive recoil and thelike. A significant advantage of the present invention arising from thevertical separation of crimping wheel sets is that stents that areunusually long are manageable and easy to crimp in a progressive manner.Typically, when long stents are crimped, it is difficult to maintaincontrol of the stent which may tend to elastically expand slightly afterinitial crimping. When such happens in an uncontrolled environment, theprocess may become complicated and the even outer surface of the stentmay be disrupted.

Further aspects of the invention are now described. While in oneembodiment the invention may be used to impart a purely plasticdeformation or elastic deformation to the stent during the crimpingprocess, it is also contemplated that the same invention may be used tocrimp stents that are composed of “memory” alloys such as Nitinol. Whenused on such stents, the entire device may be enclosed in a coolingenvironment (not shown) so that, as the diameter of the stent is reducedby repeated passage between the wheels, the cooling effect will causethe stent to retain its reduced diameter.

Under any of the above embodiments, once the stent has been crimped to adesired diameter, an outer sheath, such as seen in FIG. 1 as sheath 20may be inserted over the catheter and stent using conventional means.Where the stent has been crimped through plastic deformation, the sheathprotects the stent during delivery to a desired location within apatient's vascular system. Removal of the sheath permits inflation of aballoon to expand the stent to a desired diameter within thevasculature. Where the stent is made of a “memory” alloy such asNitinol, the sheath both protects the stent during delivery, and it alsorestrains the stent against premature deployment. Once the stent hasbeen delivered to a desired location in the vasculature, the sheath isremoved, allowing the stent to assume its natural configuration at theelevated body temperature of the patient. A balloon underlying the stenton the catheter may also be used to expand the stent for properdeployment in the vasculature.

The components of the present invention crimping tool 22 is preferablymade from injection molded plastics or machined from a variety ofpolymers including DELRIN or TEFLON. In alternative embodiments, rubberwheels can be used. To withstand the rigors of high production rates,the present invention crimping tool can be constructed from stainlesssteel, brass, aluminum, or the like. Lighter metals or high strengthrigid plastics can be use for portable units.

The present invention crimping tool 22 can be immersed in a fluid at avariety of temperatures or pressures, either of which is held at asteady state or is varied over time. Of course, the invention is easilyadaptable to automation.

Although the exemplary embodiments described above rely on nine evenlyarranged wheels to perform the crimping process, it is contemplated thatfewer or more wheels can be used to sequentially or simultaneouslyperform the crimping process.

In yet another embodiment (not shown), an optional funnel-like clip orthe like can be provided at the entrance of axial space 32 in each ofthe embodiments to help align and guide the stent-catheter assembly intothe rotating wheels. With use of the clip, one of the user's hands isfreed to perform other duties.

The present invention is sterilized and intended to be used in a cathlab by a trained technician or cardiologist. As will be appreciated bythose skilled in the art, the present invention crimping tool 22 isdesigned both for single use applications in a cath lab by a physician,or for multiple use applications in a sterile environment in a highvolume manufacturing facility. In such a manufacturing facility wheresterile conditions exist, the stent crimping tool 22 can be usedrepeatedly to crimp stents onto balloons until the mechanism wears out.Thus, repeated uses of the present invention are contemplated forcontrolled, sterile environments, as are single use applications whenoperated by cath lab personnel.

Furthermore, the present invention crimping tool can be used with anystent that is released without a delivery system. The crimping tool mayalso be sold alone, because its design is robust enough to undergo manyuses.

Other modifications can be made to the present invention withoutdeparting from the scope thereof. The specific dimensions, proceduralsteps, and materials of construction are provided as examples, andsubstitutes are readily contemplated which do not depart from theinvention.

1-4. (canceled)
 5. A method of crimping a prosthesis having an elongateaxis, comprising: positioning a plurality of wheels about the prosthesisso that an outer circumferential surface of each wheel is in contactwith the prosthesis; moving the prosthesis along the elongate axis;rotating each of the wheels while maintaining contact between the wheelsand the prosthesis, thereby reducing the diameter of the prosthesis;causing a first number of the wheels to no longer be in contact with theprosthesis to leave a first remainder of wheels in contact with theprosthesis; rotating each of the first remainder of wheels whilemaintaining contact between each of the first remaining wheels and theprosthesis, thereby further reducing the diameter of the prosthesis. 6.The method of claim 5, further including: causing a second number ofwheels from the first remainder of wheels to no longer be in contactwith the prosthesis, to leave a second remainder of wheels in contactwith the prosthesis; rotating each of the second remainder of wheelswhile maintaining contact between each of the second remainder of wheelsand the prosthesis, thereby yet further reducing the diameter of theprosthesis.
 7. The method of claim 6 wherein the plurality of wheels isnine in number, the first number of wheels is three, and the secondnumber of wheels is three.
 8. The method of claim 5, wherein moving theprosthesis along the elongate axis includes manipulating a mandrel uponwhich the prosthesis is mounted.
 9. A system for crimping a prosthesishaving an elongate axis comprising: a first plurality of wheels,wherein: each wheel is rotatably mounted on an axle; each wheel has anouter circumferential surface having a first width; the wheels areconfigured to be positionable in relation to each other such that adiameter of each wheel radiates outwardly from a central axis, wherebythe outer circumferential surfaces of the wheels define a first spacethat includes the central axis, the first space being configured toreceive the prosthesis during crimping; and a second plurality of wheelswherein: each wheel is rotatably mounted on an axle; each wheel has anouter circumferential surface having a second width; the wheels areconfigured to be positionable in relation to each other such that adiameter of each wheel radiates outwardly from the central axis, wherebythe outer circumferential surfaces of the wheels define a second spacethat includes the central axis, the second space being configured toreceive the prosthesis during crimping; and wherein the first width isgreater than the second width.
 10. The system of claim 9, wherein thefirst plurality is three in number.
 11. The system of claim 10, whereinthe second plurality is three in number.
 12. The system of claim 9,wherein the outer circumferential surface of each wheel of the firstplurality has a first curvature across the first width.
 13. The systemof claim 9, wherein the outer circumferential surface of each wheel ofthe second plurality has a second curvature across the second width. 14.The system of claim 13, wherein the second curvature is greater than thefirst curvature.
 15. The system of claim 9, wherein all the axles lie ina single common plane.
 16. A method of crimping a prosthesis having anelongate axis, comprising: positioning a first plurality of wheels aboutthe prosthesis so that an outer circumferential surface of each wheel isin contact with the prosthesis, each surface having a first width;moving the prosthesis along the elongate axis; rotating each of thewheels while maintaining contact between the wheels and the prosthesis,thereby reducing the diameter of the prosthesis; removing all of thefirst plurality of wheels from being in contact with the prosthesis;positioning a second plurality of wheels about the prosthesis so that anouter circumferential surface of each of the second plurality is incontact with the prosthesis, each surface having a second width lessthan the first width; moving the prosthesis along the elongate axis;rotating each of the second plurality of wheels while maintainingcontact between the wheels and the prosthesis, thereby further reducingthe diameter of the prosthesis.
 17. The method of claim 16, wherein thefirst plurality is three in number and the second plurality is three innumber.
 18. The method of claim 16, wherein the first surface has afirst curvature across the first width, and the second surface has asecond curvature across the second width, the second curvature beinggreater than the first curvature.
 19. A system for crimping a prosthesiscomprising: a first plurality of wheels, wherein: each wheel isrotatably mounted on an axle, and each axle of the first plurality liesin the same first plane; each wheel has an outer circumferentialsurface; the wheels are positioned in relation to each other such that adiameter of each wheel radiates outwardly from a central axis, wherebythe outer circumferential surfaces of the wheels define a first spacethat includes the central axis, the first space being configured toreceive the prosthesis during crimping; and a second plurality of wheelswherein: each wheel is rotatably mounted on an axle, and each axle ofthe second plurality lies in the same second plane, the second planebeing spaced apart from the first plane by a distance; each wheel has anouter circumferential surface; the wheels are positioned in relation toeach other such that a diameter of each wheel radiates outwardly fromthe central axis, whereby the outer circumferential surfaces of thewheels define a second space that includes the central axis, the secondspace being configured to receive the prosthesis during crimping;wherein the first space is larger than the second space,
 20. The systemof claim 19, wherein each of the first plurality of wheels has a firstwidth, and each of the second plurality of wheels has a second width,wherein the second width is smaller than the first width.
 21. The systemof claim 19, wherein the first plurality is three in number.
 22. Thesystem of claim 19, wherein the second plurality is three in number. 23.The system of claim 19, wherein the wheels are mounted on the axles suchthat the distance between the first plane and the second plane iscapable of being adjusted.
 24. The system of claim 19, wherein thewheels are mounted on the axles such that the distance between eachwheel and the central axis is capable of being adjusted.
 25. A method ofcrimping a prosthesis having an elongate axis, comprising: moving theprosthesis along its axis between a first plurality of wheels so that anouter circumferential surface of each of the first plurality of wheelsis in contact with the prosthesis; rotating each of the wheels whilemaintaining contact between the wheels and the prosthesis, therebyreducing the diameter of the prosthesis by a first amount; passing theprosthesis from between the first plurality of wheels to between asecond plurality of wheels, the second plurality of wheels beingsituated adjacent the first plurality; moving the prosthesis between thesecond plurality of wheels so that an outer circumferential surface ofeach of the second plurality of wheels is in contact with theprosthesis; rotating each of the second plurality of wheels whilemaintaining contact between the wheels and the prosthesis, therebyfurther reducing the diameter of the prosthesis by a second amount. 26.The method of claim 25, further including, after further reducing thediameter of the prosthesis by a second amount, passing the prosthesisinto a cylindrical sheath.
 27. The method of claim 25, furtherincluding, passing the prosthesis from between the second plurality ofwheels to between a third plurality of wheels, the third plurality ofwheels being situated adjacent the second plurality, moving theprosthesis between the third plurality of wheels so that an outercircumferential surface of each of the third plurality of wheels is incontact with the prosthesis; rotating each of the third plurality ofwheels while maintaining contact between the wheels and the prosthesis,thereby further reducing the diameter of the prosthesis by a thirdamount.
 28. The method of claim 27, further including, after furtherreducing the diameter of the prosthesis by a third amount, passing theprosthesis into a cylindrical sheath.